The present invention relates to a semiconductor laser apparatus, and a semiconductor laser module, having a structure in which structures for implementing a desirable optical output power and a high energy conversion efficiency from input electric power to output optical power are adequately combined.
Recently, with widespread use of various communication media such as the Internet, there have been increased demands for optical communication to be greater in capacity. In the optical communication in the past, at respective bands of wavelengths 1310 nm and 1550 nm where the absorption of light by an optical fiber is small, the transmission generally was performed by a single wavelength. In this system, for a greater quantity of information to be transmitted, it was necessary to install a greater number of cores of optical fibers in the transmission path, with increase in cost following increase in transmission capacity, as a problem.
For this reason, there has been applied a WDM (wavelength division multiplexing) communication system. The WDM communication system mainly employs an EDFA (Erbium Doped Fiber Amplifier), which is for a system that has a 1530-1570 nm band as an operation band, where it uses a plurality of wavelengths to perform transmission. This DWDM communication system or WDM communication system uses a single optical fiber for concurrent transmission of a plurality of optical signals different in wavelength, allowing for the network to have a greatly increased transmission capacity, without needing the installation of additional optical fiber lines (i.e., xe2x80x9cnew linesxe2x80x9d).
For excitation of the EDFA, there have been employed high-output pumping semiconductor laser modules. Among them, the 1480 nm-band pumping semiconductor laser module has advantages, such as 1) high reliability, 2) high conversion efficiency of erbium doped fiber, with merit in adaptation for the amplifier to be high of output, 3) wide absorption band of erbium doped fiber, enabling synthesis at multiple wavelengths, and 4) availability of peripheral optics such as isolators, wavelength synthesizers, and polarization synthesizers. As a result, by the use of wavelength synthesis, polarization synthesis, and the like, and by use of a plurality of pumping semiconductor laser modules, there has been implemented an pumping light source for high-output optical fiber amplifiers, and adapted for use in an optical fiber amplification system.
In general, in the semiconductor laser device (as a semiconductor laser apparatus), when injected electric current is increased, the optical output power increases. However, due to heat dissipation of the semiconductor laser device itself, a saturation in output power appears at a certain driving current, and thereafter the optical output power will not increase even with an increased driving current.
For the saturating driving current to be increased in value, the semiconductor laser apparatus had a cavity length elongated so that a desirable optical output power was obtained. On the contrary, to reduce the driving current required to obtain a desirable optical output power, there was selected an adequate cavity length, so that a semiconductor laser apparatus was configured with the selected cavity length. FIG. 14 is a graph showing a driving current vs. optical output power relationship for the cavity length of semiconductor laser apparatus taken as a parameter. For example, in case of a semiconductor laser apparatus to be adapted for an optical output power of 360 mW, a cavity length of 1200 xcexcm was adopted so that the driving current was minimized in FIG. 14.
However, elongation of the cavity length in semiconductor laser apparatus accompanied variation in physical configuration of the semiconductor laser apparatus, with a result that, in case of determination of the cavity length of semiconductor laser apparatus simply depending on driving current, the electric drive power involved increases, not simply in electric power consumed for optical output power of the semiconductor laser apparatus, but also of reactive power consumed at other parts in the semiconductor laser apparatus itself, such as due to serial resistance and thermal resistance, sometimes causing, as a problem, a reduction of the photoelectric power conversion efficiency. (The photoelectric power conversion efficiency is often defined as an optical output power of a semiconductor laser apparatus divided by electric drive power of the semiconductor laser apparatus.)
Moreover, with increase in reactive power consumed by semiconductor laser apparatus, that is, in the difference between electric drive power and optical output power, which is mainly converted to heat, there was the need for a heat dissipating structure to be large, resulting in a large-sized semiconductor laser module for incorporation of the semiconductor laser apparatus, as a problem. The prior art has not investigated or considered selecting the value of the cavity length to minimize the electric drive power or to maximize the photoelectric conversion efficiency for a given optical output power. In addition, the prior art has not investigated or considered selecting the value of other laser parameters, such as an impurity carrier concentration in an upper cladding layer of the laser, to minimize input drive power or to maximize conversion efficiency.
The present invention has been made with such points in view. It therefore is an object of the present invention to provide, in implementation of a semiconductor laser apparatus adapted for a desirable optical output power, a semiconductor laser apparatus having its electric drive power rendered minimal or its photoelectric conversion efficiency rendered maximal, as well as a fabrication method of the same, and a semiconductor laser module with the same. (The photoelectric conversion efficiency is the energy conversion efficiency of electrical power to optical power.)
To achieve the object, according to a first aspect of the invention, there is provided a semiconductor laser apparatus wherein a respective element value of the semiconductor laser apparatus is determined on the basis of relationships between respective elements of the semiconductor laser apparatus including a cavity length of the semiconductor laser apparatus and a carrier concentration of an upper cladding layer of the semiconductor laser apparatus and a photoelectric conversion efficiency or electric drive power of the semiconductor laser apparatus, for optical output power to be constant as a parameter, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power. An exemplary vicinal value is preferably within 10% of the minimum of the drive power and within 10% of the maximum of the conversion efficiency, and more preferably within 6% thereof, and most preferably within 3% thereof.
According to the first aspect of the invention, by implementation of a semiconductor laser apparatus wherein a respective element value of the semiconductor laser apparatus is determined on the basis of relationships between respective elements of the semiconductor laser apparatus including a cavity length of the semiconductor laser apparatus and a carrier concentration of an upper cladding layer of the semiconductor laser apparatus and a photoelectric conversion efficiency or electric drive power of the semiconductor laser apparatus, for optical output power to be constant as a parameter, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, it is enabled to obtain an desirable optical output power in a range over 50 mW, with a photoelectric conversion efficiency in a vicinity of a maximum or electric drive power in a vicinity of a minimum.
According to the second aspect of the invention, there is provided a semiconductor laser apparatus wherein a cavity length over 1000 xcexcm is determined on the basis of a relationship of electric drive power to a range of optical output power over 50 mW, for cavity length to be constant as a parameter in a range over 1000 xcexcm, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power.
According to the second aspect of the invention, by implementation of a semiconductor laser apparatus wherein a cavity length over 1000 xcexcm is determined on the basis of a relationship of electric drive power to a range of optical output power over 50 mW, for cavity length to be constant as a parameter in a range over 1000 xcexcm, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, it is enabled to obtain an desirable optical output power in a range over 50 mW, with electric drive power in a vicinity of a minimum.
According to a third aspect of the invention, there is provided a semiconductor laser apparatus wherein a cavity length is determined on the basis of a relationship of a photoelectric conversion efficiency to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, so that the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power.
According to the third aspect of the invention, by implementation of a semiconductor laser apparatus wherein a cavity length is determined on the basis of a relationship of a photoelectric conversion efficiency to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, so that the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, it is enabled to obtain an desirable optical output power in a range over 50 mW, with high photoelectric conversion efficiency.
According to a fourth aspect of the invention, in the above semiconductor laser apparatus, the cavity length is determined on the basis of an approximation expression making the photoelectric conversion efficiency maximal in correspondence to the desirable optical output power.
According to the fourth aspect of the invention, determination of the cavity length is based an approximation expression making the photoelectric conversion efficiency maximal in correspondence to the desirable optical output power.
According to a fifth aspect of the invention, in the above semiconductor laser apparatus, a cavity length over 1000 xcexcm is determined on the basis of a relationship of electric drive power to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power.
According to the fifth aspect of the invention, by implementation of a semiconductor laser apparatus having a cavity length over 1000 xcexcm determined on the basis of a relationship of electric drive power to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, it is enabled to obtain an desirable optical output power in a range over 50 mW, with low electric drive power.
According to a sixth aspect of the invention, in the above semiconductor laser apparatus, the cavity length is determined on the basis of an approximation expression making the electric drive power minimal in correspondence to the desirable optical output power.
According to the sixth aspect of the invention, when the cavity length is determined, it is determined on the basis of an approximation expression making an electric drive power minimal in correspondence to the desirable optical output power.
According to a seventh aspect of the invention, in the above semiconductor laser apparatus, an active layer forming a cavity with the cavity length has a strain multiple quantum well structure.
According to the seventh aspect of the invention, as an active layer forming a cavity with the cavity length, there is applied a strain multiple quantum well structure, while it is enabled even for the semiconductor laser apparatus having a strain multiple quantum well structure to obtain an desirable optical output power in a range over 50 mW, with high photoelectric conversion efficiency or low electric drive power.
According to an eighth aspect of the invention, in the above semiconductor laser apparatus, the desirable optical output power is within a range of 50 mW to 400 mW, and the cavity length is within a range of 1000 xcexcm to 1800 xcexcm, and more preferably within a range of 1000 xcexcm to 1600 xcexcm.
According to the eighth aspect of the invention, there is implemented a concrete semiconductor laser apparatus to be distinctive, particularly when letting the desirable optical output power be within a range of 50 mW to 400 mW and the cavity length be within a range of 1000 xcexcm to 1800 xcexcm, and more preferably within a range of 1000 xcexcm to 1600 xcexcm, and determining the cavity length simply from the relationship of the electric drive power to the optical output power.
According to a ninth aspect of the invention, in the above semiconductor laser apparatus, the desirable optical output power is within a range of 50 mW to 200 mW, and the cavity length is within a range of 1000 xcexcm to 1400 xcexcm.
According to the ninth aspect of the invention, there is implemented a concrete semiconductor laser apparatus to be distinctive, particularly when letting the desirable optical output power be within a range of 50 mW to 200 mW and the cavity length be within a range of 1000 xcexcm to 1400 xcexcm, and determining the cavity length simply from the relationship of the electric drive power to the optical output power.
According to a tenth aspect of the invention, in the semiconductor laser apparatus, an upper cladding layer has an impurity carrier concentration determined on the basis of a relationship of a photoelectric conversion efficiency or electric drive power to the impurity carrier concentration of the upper cladding layer, for optical output power and cavity length to be constant as parameters, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power.
According to the tenth aspect of the invention, by implementation of a semiconductor laser apparatus, an upper cladding layer has an impurity carrier concentration determined on the basis of a relationship of a photoelectric conversion efficiency or electric drive power to the impurity carrier concentration of the upper cladding layer, for optical output power and cavity length to be constant as parameters, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, it is enabled to obtain an desirable optical output power in a range over 50 mW, with a photoelectric conversion efficiency in a vicinity of a maximum or electric drive power in a vicinity of a minimum.
According to an eleventh aspect of the invention, there is provided a semiconductor laser module comprising a semiconductor laser apparatus according to any of the first to tenth aspects of the invention, an optical fiber for conducting outside laser light projected from the semiconductor laser apparatus, and an optical coupling lens system for an optical coupling between the semiconductor laser apparatus and the optical fiber.
According to the eleventh aspect of the invention, by implementation of a semiconductor laser module with an incorporated semiconductor laser apparatus according to any of the first to tenth aspects of the invention, it is enabled to obtain an desirable optical output power, with high photoelectric conversion efficiency or low electric drive power.
According to a twelfth aspect of the invention, the above semiconductor laser module further comprises a temperature controller for controlling a temperature of the semiconductor laser apparatus, and an optical fiber grating formed in a vicinity of an incidence end of the optical fiber.
According to the twelfth aspect of the invention, an optical fiber grating is formed in a vicinity of an incidence end of the optical fiber, and laser light of a wavelength selected by the optical fiber grating is output.
According to a thirteenth aspect of the invention, the above semiconductor laser module further comprises a temperature controller for controlling a temperature of the semiconductor laser apparatus, and an isolator disposed in the optical coupling lens system, for suppressing an incidence of reflection return light from an optical fiber side.
According to the thirteenth aspect of the invention, by implementation of a semiconductor laser module with an incorporated semiconductor laser apparatus according to any of the first to tenth aspects of the invention, it is enabled even for the semiconductor laser module with an incorporated temperature controller to obtain an desirable optical output power, with high photoelectric conversion efficiency or low electric drive power.
According to a fourteenth aspect of the invention, there is provided a fabrication method for a semiconductor laser apparatus, comprising a relationship acquiring step for acquiring relationships between respective elements of the semiconductor laser apparatus including a cavity length of the semiconductor laser apparatus and a carrier concentration of an upper cladding layer of the semiconductor laser apparatus and a photoelectric conversion efficiency or electric drive power of the semiconductor laser apparatus, for optical output power to be constant as a parameter, an element value determining step for determining a respective element value of the semiconductor laser apparatus to be determined on the basis of the relationships acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, and a forming step for forming the semiconductor laser apparatus having the respective element value determined by the element value determining step.
According to the fourteenth aspect of the invention, for fabrication of a semiconductor laser apparatus, in a relationship acquiring step there are acquired relationships between respective elements of the semiconductor laser apparatus including a cavity length of the semiconductor laser apparatus and a carrier concentration of an upper cladding layer of the semiconductor laser apparatus and a photoelectric conversion efficiency or electric drive power of the semiconductor laser apparatus, for optical output power to be constant as a parameter, in an element value determining step there is determined a respective element value of the semiconductor laser apparatus to be determined on the basis of the relationships acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, and in a forming step there is formed the semiconductor laser apparatus having the respective element value determined by the element value determining step.
According to a fifteenth aspect of the invention, there is provided a fabrication method for a semiconductor laser apparatus, comprising a relationship acquiring step for acquiring a relationship of electric drive power to a range of optical output power power over 50 mW, for cavity length to be constant as a parameter in a range over 1000 xcexcm, a cavity length determining step for determining a cavity length over 1000 xcexcm to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, and a forming step for forming the semiconductor laser apparatus having the cavity length determined by the cavity length determining step.
According to the fifteenth aspect of the invention, for fabrication of a semiconductor laser apparatus, in a relationship acquiring step there is acquired a relationship of electric drive power to a range of optical output power over 50 mW, for cavity length to be constant as a parameter in a range over 1000 xcexcm, in a cavity length determining step there is determined a cavity length over 1000 xcexcm to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, and in a forming step there is formed the semiconductor laser apparatus having the cavity length determined by the cavity length determining step.
According to a sixteenth aspect of the invention, there is provided a fabrication method for a semiconductor laser apparatus, comprising a relationship acquiring step for acquiring a relationship of a photoelectric conversion efficiency to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, a cavity length determining step for determining a cavity length to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, and a forming step for forming the semiconductor laser apparatus having the cavity length determined by the cavity length determining step.
According to the sixteenth aspect of the invention, for fabrication of a semiconductor laser apparatus, in a relationship acquiring step there is acquired a relationship of a photoelectric conversion efficiency to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, in a cavity length determining step there is determined a cavity length to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, and in a forming step there is formed the semiconductor laser apparatus having the cavity length determined by the cavity length determining step.
According to a seventeenth aspect of the invention, the above fabrication method for a semiconductor laser apparatus further comprises an approximation expression calculating step for determining an approximation expression for making the photoelectric conversion efficiency maximal in correspondence to the desirable optical output power, on the basis of the relationship acquired by the relationship acquiring step, and the cavity length determining step determining the cavity length on the basis of the approximation expression.
According to the seventeenth aspect of the invention, an approximation expression calculating step determines an approximation expression for making the photoelectric conversion efficiency maximal in correspondence to the desirable optical output power, on the basis of the relationship acquired by the relationship acquiring step, and the cavity length determining step determines the cavity length on the basis of the approximation expression.
According to an eighteenth aspect of the invention, there is provided a fabrication method for a semiconductor laser apparatus, comprising a relationship acquiring step for acquiring a relationship of electric drive power to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, a cavity length determining step for determining a cavity length over 1000 xcexcm to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, and a forming step for forming the semiconductor laser apparatus having the cavity length determined by the cavity length determining step.
According to the eighteenth aspect of the invention, for fabrication of a semiconductor laser apparatus, in a relationship acquiring step there is acquired a relationship of electric drive power to a range of cavity length over 1000 xcexcm, for optical output power to be constant as a parameter in a range over 50 mW, in a cavity length determining step there is determined a cavity length over 1000 xcexcm to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, and in a forming step there is formed the semiconductor laser apparatus having the cavity length determined by the cavity length determining step.
According to a nineteenth aspect of the invention, the above fabrication method for a semiconductor laser apparatus further comprises an approximation expression calculating step for determining an approximation expression for making the electric drive power minimal in correspondence to the desirable optical output power, on the basis of the relationship acquired by the relationship acquiring step, and the cavity length determining step determining the cavity length on the basis of the approximation expression.
According to the nineteenth aspect of the invention, an approximation expression calculating step determines an approximation expression for making the electric drive power minimal in correspondence to the desirable optical output power, on the basis of the relationship acquired by the relationship acquiring step, and the cavity length determining step determines the cavity length on the basis of the approximation expression.
According to a twentieth aspect of the invention, in the above fabrication method for a semiconductor laser apparatus, an active layer forming a cavity with the cavity length has a strain multiple quantum well structure.
According to the twentieth aspect of the invention, as an active layer forming a cavity with the cavity length there is applied a strain multiple quantum well structure, while it is enabled even for the semiconductor laser apparatus having a strain multiple quantum well structure to obtain an desirable optical output power in a range over 50 mW, with high photoelectric conversion efficiency or low electric drive power.
According to a twenty-first aspect of the invention, there is provided a fabrication method for a semiconductor laser apparatus, comprising a relationship acquiring step for acquiring a relationship of electric drive power to an impurity carrier concentration of an upper cladding layer, for optical output power and cavity length to be constant as parameters, a carrier concentration determining step for determining the impurity carrier concentration to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power; and a forming step for forming the semiconductor laser apparatus with the upper cladding layer having the impurity carrier concentration thereof set to the impurity carrier concentration determined by the carrier concentration determining step.
According to the twenty-first aspect of the invention, for fabrication of a semiconductor laser apparatus, in a relationship acquiring step there is acquired a relationship of electric drive power to an impurity carrier concentration of an upper cladding layer, for optical output power and cavity length to be constant as parameters, in a carrier concentration determining step there is determined the impurity carrier concentration to be determined on the basis of the relationship acquired by the relationship acquiring step, so that the electric drive power is vicinal to a minimum thereof in correspondence to a desirable optical output power, and in a forming step there is formed the semiconductor laser apparatus with the upper cladding layer having the impurity carrier concentration thereof set to the impurity carrier concentration determined by the carrier concentration determining step.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.